Earth drilling apparatus and method

ABSTRACT

Well drilling and well casing placement are carried out by a process in which a drill string and surrounding casing are advanced while being rotated, preferably in opposite directions. The process is preferably carried out using a drill rig having a mast that is movable along its direction of elongation and a casing rotation table fixed to the mast.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from provisional application No. 61/491,487, filed May 31, 2011.

FIELD OF THE INVENTION

This invention relates to earth drilling, and particularly to improvements by which insertion of well casing can be carried out more efficiently.

BACKGROUND OF THE INVENTION

A water well is typically drilled by a portable drill rig having a mast. The drill stem, composed of one or more lengths of drill pipe, and having a cutting bit at one end, is rotated by a top head connected to the opposite end of the drill stem. The top head is movable lengthwise along the mast, and descends with the drill stem as drilling proceeds. When a major part of the length of an uppermost length of pipe in the drill stem is in the bore hole and the top head is near the lower end of the mast, the top head is disconnected from the drill stem, and moved upward toward the upper end of the mast. Another length of drill pipe is then moved into place between, and connected to, the top head and the part of the drill stem extending upward from the bore hole, and drilling is resumed.

In well drilling, it is common practice to use well casing to prevent collapse of the walls of a borehole while drilling is taking place. A well casing is typically composed of one or more lengths of pipe having a diameter greater than that of the drill pipe.

In order to set well casing in place, the bore hole is first drilled to the desired depth of the casing using a bit having a diameter that is larger than the diameter of the casing. When the bore hole reaches the desired casing depth, the drill string is withdrawn from the bore hole. As the drill string is withdrawn, drill pipe sections are removed from the drill string one section at a time until the drill string, including the bit, are removed from the hole. Then, the casing sections are introduced one section at a time through an opening in a drive table movable along the mast of the drill rig. The first section of casing to be introduced is lowered down the open hole, supported by a plate lifting device hooked to a cable attached to a jib boom.

The lengths of casing can be brought into position above the table by means of pipe-handling arms, or alternatively by a cable connected to a jib boom. The lengths of casing can then be aligned with the bore hole by hand, while still attached to the cable.

Each length of casing is typically provided with a tab welded near its upper end for engagement with the table in order to prevent the casing from being dropped into the bore hole. When each length of casing is introduced to the extent such that its tab is in, or nearly in, engagement with the table and the table is in its lowermost position, a next length of casing is attached to the casing already in place, usually by welding, but sometimes by engagement of threads on the casing sections. After the attachment is completed, the tab is cut off and the insertion of the casing is continued. When the casing is in place, grout is introduced into the space surrounding the casing. Then, drilling is continued, using a bit having a diameter smaller than the internal diameter of the casing.

The conventional process is particularly time-consuming because it requires disassembly and removal of the drill string after the casing bore is drilled and reassembly of the drill string in order to continue drilling beyond the lower end of the casing. There is also a risk that the casing will be accidentally dropped into the casing bore necessitating retrieval, which can be difficult.

SUMMARY OF THE INVENTION

A first aspect of the invention is a method in which the introduction of casing is carried out simultaneously with drilling, thereby avoiding the time-consuming steps of removing the drill string from the casing bore before the casing is introduced, and reassembling the drill string for further drilling beyond the lower end of the casing.

More particularly, drilling of a well is carried out using a drill rig comprising an elongated mast having upper and lower ends, a mast support, a top head for rotating a drill string, the top head being movable lengthwise along the mast, and a casing rotator connected to the mast. The casing rotator includes a rotatable chuck for gripping and rotating a length of well casing. The drilling process comprises the following sequence of steps. A length of drill pipe is connected to the top head. A length of well casing is then slid onto the length of drill pipe connected to the top head until the end of the length of drill pipe remote from the top head is exposed. The length of drill pipe is then connected to the upper end of a drill string already in a bore hole, thereby lengthening the drill string. The length of well casing is connected to the upper end of a well casing surrounding the drill string thereby lengthening the well casing. The drill string has a cutting bit at its lower end, and the well casing surrounding the drill string has a drive shoe at its lower end. Drilling of the well is carried out by rotating the drill string by means of the top head, and simultaneously rotating and lowering the well casing into the well by means of the casing rotator. The foregoing sequence of steps is repeated until the well casing is inserted to a desired depth.

After the repetition of the above-described sequence of steps is discontinued, and, with the well casing inserted to the desired depth, drilling can be continued by connection of additional lengths of drill pipe to the drill string, and rotating the drill string by means of the top head.

The steps of rotating the drill string by means of the top head, and simultaneously rotating and lowering the well casing, are preferably carried out by rotating the drill string and well casing in opposite directions.

A second aspect of the invention is a drill rig construction which is better adapted to the above-described simultaneous drilling and casing introduction method. Preferably, the casing rotator is fixed to the mast, the mast is movable lengthwise relative to the mast support, and the well casing is lowered by repeatedly moving the mast lengthwise relative to the mast support, and relative to the top head.

More particularly, a drill rig in accordance with this second aspect of the invention comprises an elongated mast, a mast support, a top head for rotating a drill string, the top head being movable lengthwise along the mast, and a casing rotator having a rotatable chuck for gripping and rotating a length of well casing. The casing rotator is mounted at a fixed position along the length of the mast, and the mast is movable relative to the mast support along the mast's direction of elongation. A well casing can be advanced into a well by simultaneous rotation of the chuck and lengthwise movement of the mast. The well casing is advanced by gripping the casing with the chuck of the casing rotator, and rotating the casing while simultaneously lowering the mast. When the casing rotator reaches the lower limit of its range of movement, the grip of the casing rotator on the mast is released, the mast is raised, and the grip of the casing rotator on the casing is reestablished so that further advancing movement of the casing can take place by lowering of the mast.

The top head, which rotates the drill string, is guided by the mast, but the mast and top head move independently along the direction of the length of the mast. Consequently, drilling can proceed continuously while the well casing is being advanced by up and down movement of the mast, being interrupted only for the insertion of additional lengths of drill pipe and additional lengths of well casing.

The fact that the casing rotator is located at a fixed position along the length of the mast ensures that it does not interfere with the movement of lengths of drill pipe and lengths of well casing into alignment with the drill string and casing, respectively already in place. Traditional pipe handling equipment and techniques can therefore be used. In addition, since drilling and advancement of the casing take place simultaneously, the top head can remain substantially at a constant position on the mast throughout the portion of each drilling cycle during which the mast is moving downward to advance the casing. Consequently, it becomes easier to control the advancing movement of the drill string and the casing.

Objects and other advantages of the invention will be apparent from the following description when read in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-8 are perspective views of a drill rig in accordance with the invention, showing successive stages of the process of introducing a length of well casing into a bore hole.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, the drill rig comprises an elongated mast 20 mounted on a transporting vehicle 22, in this case a track-driven vehicle. A top head 24 for rotating a drill string is provided on the mast. The top head is guided for movement lengthwise along the mast, and movable along the mast by chains (not shown) driven by a hydraulic motor (not shown).

The top head 24 is pivoted so that it can be tilted as shown in FIG. 1 to a condition such that a length 26 of drill pipe connected to the top head can be brought to a nearly horizontal condition when the top head is moved to a position near the lower end of the mast. When the drill pipe is in its nearly horizontal condition, a length 28 of well casing can be slid onto the drill pipe as shown in FIG. 2.

The length of well casing can be drawn onto the length of drill pipe by a cable (not shown) having a hook that engages the end 30 of the casing. The cable extends from a jib boom (not shown) on the mast and the casing is drawn onto the drill pipe by operation of a winch around which the cable is wound.

When the upper end of the length of well casing is adjacent the top head, the top head is raised as shown in FIG. 3, and the length of drill pipe and the surrounding length of well casing are gradually drawn upward and into a condition in which they are parallel to the mast as shown in FIG. 4. At this time, the drill pipe and casing are both aligned with an opening in a table 32, which is fixed to the mast 20 at or near the lowermost end of the mast, and a portion of the length 26 of drill pipe extends beyond the lower end of the length of casing.

In the first stage of the drilling process, that is, when the length of drill pipe 26 is to be the lowermost length of drill pipe in the drill string and the length of well casing 28 is to be the lowermost length of casing, a bit will be connected to the lower end of the length of drill pipe. The diameter of the bit should be less than the inner diameter of the well casing so that the bit and drill string can be withdrawn when drilling is completed, or for replacement of the bit. Alternatively, a collapsible bit having a diameter larger than the internal diameter of the casing can be used. The casing will include a drive shoe, and because the casing will participate in drilling by enlarging the bore hole formed by the drill bit, the drive shoe will preferably have a circle of hardened cutting teeth surrounding its end opening. The toothed drive shoe can be an integral part of the lowermost length of casing, or can be supplied as a short element for attachment to a standard length of casing.

The table 32, as shown in FIG. 4 has a central opening in which a casing rotator 34 is situated. The casing rotator comprises a set of jaws which can be made to contract by hydraulic actuators in order to grip a length of well casing, and which can be made to rotate by a hydraulic motor (not shown) in the table 32. The top head and casing rotator should rotate in opposite directions. Preferably, the top head should rotate clockwise (looking down) to maintain a tight connection between the threads of the top head and the uppermost length of pipe in the drill string, and between the connecting threads of the lengths of pipe in the drill string. The casing rotator should rotate in the opposite direction, i.e., counterclockwise, so that friction between the casing and the drill string does not accidentally cause disconnection of the drill string from the top head or disconnection of drill pipes from one another.

The cutting bit can be attached to the exposed lower end of the length 26 of drill pipe either before or after the casing is moved through the casing rotator by lowering of the top head along the mast. The drill pipe and the length of casing are lowered through the casing rotator and the casing is held by casing clamps (not shown) underneath the casing rotator while the cable is disconnected from the lower end of the casing.

After the cutting bit is in place as shown in FIG. 5, and with the mast in its raised condition and the jaws of the casing rotator clamped onto the length 28 of casing, drilling and advancing of the casing can commence by simultaneously lowering the mast, rotating the drill pipe clockwise and rotating the casing counterclockwise.

FIG. 6 shows an early stage in the drilling operation, in which the mast is moving downward and approaching its lowermost position.

When the mast reaches its lowermost position, the jaws of the casing rotator are opened to release their grip on the casing, and the mast is raised so that the jaws can grip the length of casing at a higher position. As the mast is raised, the top head is allowed to remain at a fixed height so that the bit remains at the bottom of the hole being drilled. The jaws are again closed so that the casing rotator grips the casing, and simultaneous drilling and advancing movement of the casing are resumed and continued until the mast once again reaches its lowermost position as shown in FIG. 7, whereupon the jaws are again opened, the mast is moved upward as shown in FIG. 8, the jaws are reengaged with the casing, and drilling and advancing movement of the casing are continued.

When the first length of casing is advanced to a position such that its upper end is a short distance above the upper side of the casing rotator and the mast is at or near its lowermost position, another length of drill pipe and another length of casing can be attached respectively to the first length of drill pipe and to the first length of casing. A hydraulically operated holding fork is extended from the rotator housing, and aligned with flats on the drill pipe in order to grip the length of drill pipe in the hole and allow the top head to disconnect from the drill pipe. A new length of drill pipe is then moved into place and attached to the top head. The attachment of the new length of drill pipe can be carried out by moving the top head upward on the mast and bringing the new length of drill pipe from a storage rack or carousel into position underneath the top head using any of various known types of drill pipe handling equipment, for example the equipment described in International Patent Publication No. WO 98/55728, Published Dec. 10, 1998. The new length of drill pipe is connected to the top head, and then connected by threads to first length of drill pipe. The top head can then be lowered while the top head and the length of drill pipe connected to it are tilted, so that the drill pipe is brought to a near horizontal condition as in FIG. 1. A second length of casing can then be slid onto the drill pipe as in FIG. 2, and the drill pipe and the surrounding length of casing can be drawn upward as in FIG. 3 to a condition in which they are parallel to the mast in FIG. 4 and aligned with the opening in the casing rotator. At this time, the second length of drill pipe is attached to the first length of drill pipe by threads, and the second length of casing is attached to the first length of casing either by welding, or by threads if threaded casing is used. Simultaneous drilling and advancing movement of the casing can then be resumed, following essentially the same procedure as described above and depicted in FIGS. 1-8.

Additional lengths of drill pipe and casing can be inserted in the same manner in which the second lengths of drill pipe and casing are inserted. When the casing reaches the desired casing depth, the space surrounding the casing can be filled with grout, and drilling can be continued to a desired depth below the lower end of the casing by the addition of more lengths of drill pipe to the drill string.

When the well reaches the desired depth, the drill string is withdrawn. The drill bit can be withdrawn through the casing, since its diameter is less than the internal diameter of the casing. Alternatively various kinds of collapsible bits, such as an “underreaming” bit, can be used, in which case the diameter of the bit, while drilling is taking place can be greater than the internal diameter of the casing.

The well drilling process according to the invention is more efficient than conventional drilling because advancing movement of the casing and drilling are carried out simultaneously, obviating the time-consuming withdrawal of the drill string following the drilling of a casing bore and prior to the introduction of the well casing. The process can also be carried out using casings without supporting tabs and eliminates the step of cutting the supporting tabs off the lengths of well casing. Although it is possible to carry out the process using conventional drilling equipment, the use of a drill rig in which the mast is movable lengthwise and the casing rotation table is fixed to the mast enables the simultaneous drilling and casing advancement to be carried out with still greater efficiency. 

1. A process for drilling a well using a drill rig comprising an elongated mast having upper and lower ends, a mast support, a top head for rotating a drill string, the top head being movable lengthwise along the mast, and a casing rotator connected to the mast, the casing rotator having upper and lower sides and a rotatable chuck for gripping and rotating a length of well casing, the process comprising a sequence of steps in which: a length of drill pipe is connected to the top head; a length of well casing is slid onto said length of drill pipe while the length of drill pipe is connected to the top head until the end of said length of drill pipe remote from the top head is exposed; the length of drill pipe is connected to the upper end of a drill string having a cutting bit at its lower end, thereby lengthening the drill string; the length of well casing is connected to the upper end of a well casing surrounding the drill string, said well casing surrounding the drill string having a drive shoe at its lower end, thereby lengthening the well casing; drilling of the well is carried out by rotating the drill string by means of the top head, and simultaneously rotating and lowering the well casing into the well by means of the casing rotator; the process further comprising: repeating the foregoing sequence of steps until the well casing is inserted to a desired depth.
 2. The process according to claim 1, in which the repetition of said sequence of steps is discontinued, and, with the well casing inserted to said desired depth, drilling is continued by connection of additional lengths of drill pipe to the drill string, and rotating the drill string by means of the top head.
 3. The process according to claim 1, in which the casing rotator is fixed to the mast, the mast is movable lengthwise relative to the mast support, and the well casing is lowered by repeatedly moving the mast lengthwise relative to the mast support, and relative to the top head.
 4. The process according to claim 1, in which the step of rotating the drill string by means of the top head, and simultaneously rotating and lowering the well casing are carried out by rotating the drill string and rotating the well casing in opposite directions.
 5. A process for drilling a well using a drill rig comprising an elongated mast having upper and lower ends, a mast support, a top head for rotating a drill string, the top head being movable lengthwise along the mast, and a casing rotator having upper and lower sides and a rotatable chuck for gripping and rotating a length of well casing, wherein the casing rotator is mounted at a fixed position along the length of the mast, and wherein the mast is movable relative to the mast support along the mast's direction of elongation, the process comprising: connecting a first length of drill pipe to the top head; sliding a first length of well casing onto said first length of drill pipe while the length of drill pipe is connected to the top head until the end of said first length of drill pipe remote from the top head is exposed, said first length of well casing having an upper end and a lower end, the lower end being in the form of a drive shoe having an annular cutting bit; passing a part of the first length of well casing and a part of the first length of drill pipe extending through the first length of well casing through the casing rotator; with a bit attached to said end of the length of drill pipe, causing the top head to rotate the first length of drill pipe and causing the casing rotator to rotate the first length of well casing while lowering the mast along the mast's direction of elongation toward a lowered condition, thereby simultaneously forming a bore hole with said bit, enlarging the bore hole with said drive shoe, and introducing the first length of well casing into the bore hole; repeatedly disengaging the casing rotator from the length of well casing, raising the mast and the casing rotator while allowing the top head to remain at a substantially constant height, reengaging the casing rotator with the length of well casing and resuming rotation of the well casing, thereby continuing the simultaneous formation of the bore hole, enlargement thereof and introduction of the length of well casing; when the casing rotator is in its lowered condition and the upper end of the first length of casing and the top head are both located adjacent the upper side of the casing rotator, disconnecting the top head from the drill pipe, raising the top head on the mast, attaching an additional length of drill pipe to the top head, sliding an additional length of well casing onto said additional length of drill pipe attached to the top head, connecting the additional length of drill pipe to the first length of drill pipe, connecting the additional length of well casing to the first length of well casing; and resuming simultaneous drilling, bore hole enlargement and well casing insertion by causing the top head to rotate the connected lengths of drill pipe and causing the casing rotator to rotate the connected lengths of well casing; and repeatedly disengaging the casing rotator from the additional length of well casing, raising the mast and the casing rotator while allowing the top head to remain at a substantially constant height, reengaging the casing rotator with the additional length of well casing, and resuming rotation of the well casing, thereby continuing the simultaneous formation of the bore hole, enlargement thereof, and introduction of the length of well casing.
 6. The process according to claim 5, in which the step of causing the top head to rotate the first length of drill pipe and causing the casing rotator to rotate the first length of well casing, and the step of causing the top head to rotate the connected lengths of drill pipe and causing the casing rotator to rotate the connected lengths of well casing, are both carried out by rotating the top head and casing rotator in opposite directions.
 7. A drill rig comprising: an elongated mast; a mast support; a top head for rotating a drill string, the top head being movable lengthwise along the mast; and a casing rotator having a rotatable chuck for gripping and rotating a length of well casing; wherein the casing rotator is mounted at a fixed position along the length of the mast; and wherein the mast is movable relative to the mast support along the mast's direction of elongation, whereby a casing can be moved into a well by simultaneous rotation of the chuck and lengthwise movement of the mast.
 8. A drill rig according to claim 7, in which the top head and casing rotator are capable of rotating in opposite directions. 